Magnetron modulation system



Nov. 1, 1938. M. PONTE ET AL 2,135,199

MAGNETRON MODULAT I ON SYSTEM Filed Nov. 6, 1936 Fig.1

MAGNUM-3 a; 05m 3 2* MODl/ZAT/A POIFIWYAL INVENTORS M- I U/V75 L. -Z/E BY ATTORNEY Patented Nov. 1, 1938 creme MAGNETRON ODULATION-SYSTEM v Maurice Ponte and; Iiuc Maurice Elie, Paris,

France, assignors: to: Compagnie; Generale de. Telegraphic Sans Fil, a corporationoflErance Application- November 6, 1936; Serial N0.- 109,400

' InFranoe Novemben'l, 1935' e 2 Claims..

means designedtomake the starting of oscillations in telegraph transmitters or oscillatorsknown in the art as magnetron transmitters subject to the control oi" modulation voltage;

more'anodes placed" inside avacuous container in the presence of an electronemitting cathode,

when suitably placed within a magnetic field will'produce oscillations in a circuit connectedwithsaid anodes.

The produced oscillations may cover an extremely wide band or range' of frequencies. The inventionis more particularly useful in the case of waves known as short waves,-thoughit maylikewise be applied to the whole spectrum of frequencies which these oscillators will produce.

In describing myinvention-referencewill be madeto the attached drawing wherein Figure 1 illustrates a magnetronoscillator-and control means therefor, arranged in accordance with the present invention; Figure's 2,. 3, 4, and *are graphs or curves illustrating the operating characteristics of the magnetron oscillator in the presence of a-variable anode potential we variable field or both, while, Figure fi illustrates a I signalling system including modulating means connected with the magnetronoscillator-of the present invention.

Figure 1- shows schematically a magnetronM' 7 The magnetron M'consisting of anodes l-and fil-fament 2is placed-inside a magnetic fieldlH and with it circuits 3 and sources 4] and Ill are ar ranged to excite oscillations in circuit 3; The

magnetron plates! are-fed from'generator 4 setting up a positive potential denoted by V while the current producedby thesaid generator is The. oscillating. current meas- It isknown from the practice of producing oscillationsthat a magnetron comprising one or (01.179-171) '7 The present invention" concerns ways and The characteristics of the oscillator will now be described." They will be clearlyunderstood by reference to Figures 2 and 3 which'represent the variations:of-I;3andIl as-a function of- Vp. With; the magnetic-afield H being stabilized or fixed; theassumption-shall be made that the'potential V5-isgradually raised from zero. For a certainvalue of V Ip rises but slowly until, in thepresenceof an-extremely small variation of voltage -Vp; itssuddenly rises to" the maximum value of "electron emission of the filament 'known as the saturation current and herein designated as Is; the plate currentthereafter remaining constantor-unvaried as-V increases; The oscillating current IA' commences as Vp begins to" grow, and suddenly rises 1 with increased Vp, and

passes through abroad maximum and finally decreases as V 5 continues to grow; However, the fall of the value-of-the-current IA is slower and more gradual than its first appearance and rise with growth-ofV Figure-3- shows the same characteristics taken forgrowingwa-lues- H1 I-Iz- H3 H4 of the magneticfieldT-l. These characteristics are plotted while disregarding possible hysteresis of the device'which produces the magnetic field H..

The graph in Figure 4 shows" whathappens when, V is held constant or stable-and H- is varied. As the-field I-I'growsgradually from zero; theoscillatory current IA starts to flow when the field has attained; the value H1. The current IA; grows linearly fromzero as the field grows, passes through a broad [ma-Ximum; decreases thereafter, and disappears suddenly in the presence of a field intensity 1-12.

The anode current'I which initially is' equal tothe saturation current Is" decreases later at aboutthe-sametiine-as IA and it disappears after the latter.

Figure B-shows the same characteristic curves taken withgrowing values of V1, V2, V3, V4, etc., of the anode potential Vp.

In-the light of what precedes it maybe said, as shownin-Figure that the graph giving the var'iationsof IA as a function of H, comprises two zones; namely, one extending'from O to H1 and theotherfrom Hzto-infi'nity where the oscil-- latorycurrent is zero.

Now, according to the: present" invention this propertyv is utilizedfor the automatic control'of the initiation of oscillations by the modulation voltage. Intact; the useof this property makes the transmitter is being modulated; for as. .soon

as:- this :rnodulationiceasesg:.thesev oscillations auitifeasiblefor the oscillations to begin only when tomatically discontinue as they are no longer produced.

In order to modulate a magnetron oscillator, the field H and the plate or anode voltage Vp are regulated in such a way that .the strength I11 of the oscillation current lies between the points MA and N of the curve IA=f (Vp) represented in Figure 2. To this point corresponds the anode voltage V and the field Ho. There is then superposed upon V11 the desired alternating modula-;

tion potential, this resulting in a variation of the amplitude of IA in proportion to the amplitude of this modulation potential and at the same frequency.

Referring to curve IA=f (H) of Figure 4 in i which is shown the field Ho corresponding to the the requisite change in the magnetic field is smaller, and the operating point of the'magnetron while the blocking action persists, stays inside a region where the oscillations are very stable.

Whichever method may beused, variation of the magneticfield is secured by the aid of an auxiliary coil which is connected in the magnetic circuit and which contains the number of ampere turns required for the production of the field variation in question. These ampere turns are opposition to the field Ho.

the principle before described, would likewise fall inside the scope of the invention.

In Figure 6 is shown a magnetron M comprising a field coil N setting up the fixed field Ho and a coil N2 producing the auxiliary blocking, field Hm. This, field Hm in this embodiment is in The coil N2 is traversed by the plate current of tube L3 whose plate is connected by N2 to a point on resistance 20 in shunt to a source of potential 22.

The magnetron M is modulated on its anode electrodes by the tube L1, the modulation potential being applied from any source to the primary of transformer T1. The secondary of the said transformer T1 also excites the control grid of amplifier tube L2 whose plate is connected with transformer T2. The secondary of this transformer is closed upon a resistance R by way of a rectifierD. The rectifier D may be either a contact type detector or a diode. If the latter is provided, it may be combined with tube L3 and both D and L2 may be confined inside one and the same bulb or envelope. The resistance R is connected between the grid and the cathode of the tube L3 so that when the rectifier is operative, the grid of tube L3 is rendered negative. In the absence of current through D the grid of L3 is less negative and plate current flows in L3 and N2 to produce a field opposing the fieldof N1, 7 The condenser 0 serves the purpose of imparting a certain time constant to the assembly. For simplicity the filament heating circuits for M L1 La and L3 have been omitted.

The operation of the arrangement is as folrows:

In the absence of modulation potentials in T1, the oscillations in M and 3 are blocked by the auxiliary field produced by the plate current of tube L3 through the coil N2 which opposes the field produced by N1. When a modulation voltage is applied to the primary of transformer T1, the same will be amplified by L2 and rectified by D. The result is that the grid of L3 becomes negatively biased. 'Ihis biasing action has been adjusted in-such a fashion that it will be sufficient to block the 'fiow of plate current in L3, even for very low potentials applied to T1. In these conditions the auxiliary field produced by N2 is eliminated or suppressed and the magnetron may be considered as operating at, say, point Ho of Figure land is capable of oscillating. The modulating potentials are at this time acting through T1, L1 and the coupling 30 to modulate the anodes l of M. As to the plate potential plate alternating current characteristics, the tube may now be considered as operating between MA and N of Figure 2. The ensuing oscillations will persist as long as the modulation lasts, and they will disappear as soon as modulation ceases. The values of R andof C may be regulated in such a way that the starting of oscillations is able to follow the rhythm of an intermittent modulation such as a telephone conversation. In these conditions the oscillator is readily adapted to the establishing of duplex telephony on one and the same wave-length, with the sending and receiving antennae placed at close proximity to each other.

The transmitter is then blocked during the receiving intervals and blocked during sending intervals, while the opposite happens in the receiver. The blocking and unblocking of the receiver are then subject to the control of the transmitter using an arrangement similar to the one before described. All that is necessary is to provide the transformer T2 with another secondary close-d upon the rectifier and apply the rectified. voltage, in-suitable sense, to the grids of the amplifier tubes in thereceiver.

, Although magnetron tube arrangements of different structural dimensions may be used, we have found that a tube structure having the following dimensions operates satisfactorily: Anode diameter 5mm. cathode axially arranged within the anode; plate voltage (optimum value at rest) 550 volts; magnetic field 780 gauss. The oscillator circuit may comprise two parallel rods or conductors of 3mm. diameter separated by 25 mm. Oscillations of a wave-length of 85 cm. are produced. 7

We claim:

1. In a 'telegraphy system, a tube having an anode and a cathode connected in an oscillatory circuit, means for applying energizing currents to said electrodes, means for producing a magnetic field surrounding said electrodes of sufficient value to produce oscillations in said tube and circuit, means for opposing said field by an additional field of sufiicient value to stop oscillations in said tube and circuit, and means for modulating. said additional field in accordance with signals to produce oscillatory energy in said tube andcircuit characteristic of said signals.

2. In a signalling system, a source of modulating potentials, an' electron discharge tube hav-' ing an anode and a cathode electrode, an oscillatory circuit connecting said anode and cathode, means for applying energizing currents to said anode and cathode and a magnetic field to said electrodes, whereby oscillations are produced in said tube and circuit, means for producing an additional field opposing said first field an amount sufiicient to prevent the production of oscillations in said tube and circuit, means connected with said last named means and with said source of signals for reducing said last named field in the presence of signaling energy, and means connected with the anode of said tube and with said source of signals for modulating the anode potential of said tube in accordance with signals.

' MAURICE PONTE.

LUC MAURICE ELIE. 

